Teaching about Time

Noah Fay, Science Department, Pima Community College and University of Arizona

Below is an itemization of the challenges I encounter and methods I use (or don't use, as the case may be) in teaching temporal concepts. They are all in the context of geologic time and the techniques used therein. For some context, these are all related to a 15-week Physical Geology class at Pima CC where I have usually 2 class periods w/labs (total ~5 hrs) to cover the topics.

  • The limited time in which to teach about time: I have one class period for discussion of deep time, the geologic time scale, etc., and one class period for absolute time. This isn't enough to do either justice, but with other instructional constraints, I do not have more time and therefore do not have a strategy to solve this problem.
  • What does 4.6 billion years really mean?: Grasping the immensity of geologic time is difficult for people who normally don't deal with such large numbers. I use a number of strategies such as 1) a rope with geologic events to illustrate the gaps in time between them, 2) an analogy with a calendar and earth's history spread over 1 calendar year, and 3) various analogies of "everyday" items and the relation to 4.6 billion of them (see screenshot of two ppt slides below). Overall I think the analogies and calendar example are the most effective in illustrating the scale of geologic time.
  • Radioactive decay and absolute age determination: I have yet to encounter (or develop myself) an effective lab exercise on this topic. I have used an exercise that involves paper "coins" that when randomly flipped simulate radioactive decay and parent to daughter conversion. I think the exercise is instructive, but it's also rather tedious and isn't the best use of class time. I would like to leave the workshop with ideas for a new activity.
  • Religious biases against radioactive dating: There are many websites/books/articles providing bogus information bolstering religious "arguments" questioning the validity of radioactive dating, the age of the earth, etc. Students regularly express (written or verbal) their skepticism of this portion of the class, despite my best efforts. For example, I had a very good student write on an exam that scientists do not have reliable techniques for determining the ages of rocks/earth/etc., despite having participated in the discussion and activities of radiometric dating just 10 days prior. My experience suggests that, in general, a teacher (or anyone) can't force old ideas out of someone's head and can only hope to put new ideas in. What is an instructor to do when those old ideas are in direct conflict with the new ideas? I would like to learn more about the psychological aspects of this problem.
  • Assessment: I do not have any particular assessment strategies (but would like to learn some) other than I have been experimenting with cooperative exams, which cover geologic time (and everything else in the course) and thus far the results have been positive. Quantitatively, exam scores usually improve w/the cooperative portion included, and qualitatively, the I can see that students are genuinely learning from one another during their discussions.

Slides with Analogies for Time Scale Representation

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